I have three Macs on my LAN. Call them Mini, Ret, and Flat. All three have a user named 'chap', who's an Admin. Mini and Ret are running the most current version of MacOS 10.13, and Flat is running the latest MacOS 10.14. Mini and Ret are both set to permit screen sharing. Flat is my laptop.
(Note: when I say "screen share from A to B", A is local and B is remote.)
I can screen share from Ret to Mini, from Mini to Ret, and from Flat to Mini without being prompted for username/password. When I try to screen share from Flat to Ret, though, I'm always prompted to log in.
Ret and Mini have the same System Preference > Sharing settings for screen sharing. Automatic login of 'chap' is set for all three systems.
Any thoughts why Ret is requesting logins from Flat (and not from Mini)?